Mercury Sorption by Biochars Produced From Invasive Brazilian Pepper At Different Temperatures.

Characteristics and mechanisms of mercury sorption by biochars derived from Brazilian Pepper (BP; Schinus terebinthifolius) through pyrolysis at different temperatures (300, 450, and 600¢ªC) were investigated. The Hg removal was investigated as a function of pH and contact time using batch experiment. The optimum removal conditions were pH 6.0 after 24 h. The surface characteristics of BP biochars before and after Hg sorption were examined with scanning electron microscopy-equipped with energy dispersive X-ray spectroscopy and Fourier transform-infrared spectroscopy (FTIR). The sorption process can be described by the pseudo-second order equation and Langmuir equation. The kinetic data suggested that Hg sorption was rapid and reached equilibrium after 24 h. All biochars were effective in Hg sorption, with the Langmuir maximum sorption capacity ranging from 28.6 to 41.0 mg/g and the sorption capacity decreasing as temperature increased. FTIR and chemical modification results showed that carboxylic and amine groups were responsible for Hg sorption by BP biochars and the lower the pyrolytic temperature, the more important of those function groups were. Release of Ca²⁺, K⁺ and Na⁺ cations confirmed the role of ion exchange for Hg removal by BP biochars. Our results suggest that BP biochars may have a potential as an alternative sorbent to remove Hg from waste water.